1. Field of the Invention
This invention relates to flexible circuitry and, more particularly, to devices and methods for substantially reducing failure of same resulting from excessive bending or flexing.
2. Description of Related Art
Circuitry can be arranged in a flexible form by containing the electronics within a thin, semi-flexible laminate. When so configured, as opposed to housing the circuitry within a semi-rigid printed circuit board, for example, the circuitry encounters an increased incidence of failure. The number of flexes that such circuitry can withstand before failure depends upon a number of factors, including the number of layers comprising the flexible circuitry, the thickness and width of associated circuitry elements and the sharpness of the bend, for example. Once the degree and number of bends reach a certain level, failure occurs. Such failures, which often occur in the form of a short circuit, most typically are the result of repeated or excessive flexure of the circuitry beyond elastic limit.
Certain flexible circuitry laminates include six layers, with positive and ground layers in the interior and two outer layers on either side. This particular class of circuitry can accommodate certain types of full-computer line layouts horizontally, for example in a 1.sup.3/4 " width factor. Problems arise, however, when attempting to connect flexible 6-layer circuitry to stiffer portions of the product, or to other portions possessing increased stiffness. Such stiffer portions can be fixed- or stiff-section component areas, for example, a ball grid array covering the product, or can be in close proximity to such areas.
The stiff portions of the circuitry can endure a relatively low volume of flexure before failure compared to the flexible regions of the product. Further, in multiple-layer products, in particular, the most likely failure point generally is located at a connection point between a semi-rigid region and a flexible region. The problem is exacerbated as the thickness of the circuitry decreases, for example at 18 mil or thinner, as the flexure of the circuitry persists for a longer duration in thinner layers. Accordingly, stiff circuitry portions and their connection to more flexible circuitry portions generally present difficulties in a variety of environments and applications, including wearable-computer environments.
U.S. Pat. No. 5,581,492 granted to Janik, assigned to the assignee of the present application, and incorporated by reference herein, addresses the above-described problem by illustrating a series of substantially rigid members encompassing a flexible circuitry portion along its length. In a particular embodiment, the rigid members are characterized by a curvature at each of their respective ends to limit the radius of curvature experienced by the circuitry. The rigid members are illustrated as positioned externally to the flexible circuitry. Janik does not directly illustrate association or integration of flex-limiting members into or between the layers of the flexible circuitry laminate. Further, the rigid members of Janik are illustrated with, although not limited to, a generally uniform characteristic. No direct illustration is made with regard to insertion of single or multiple members of varying shape, size, material type, or durometer value, in various combinations, configurations, and arrangements to effect different minimum bend radii for different applications.
Accordingly, a need exists for an assembly to provide a solution to the aforementioned difficulties.